Molecular characterization of plasmids encoding blaCTX-M from faecal Escherichia coli in travellers returning to the UK from South Asia.

ABSTRACT

BACKGROUND: The global prevalence of extended-spectrum beta-lactamase-producing Escherichia coli is rising and is dominated by blaCTX-M spread by plasmids. Travellers to South Asia from Western Europe have high rates of acquisition of faecal CTX-M-producing E. coli (CTX-M-EC). AIMS: To determine the conjugative ability of CTX-M-EC acquired by healthy volunteers after travel to South Asia, the proportion of travel-acquired CTX-M-EC where blaCTX-M is encoded on a plasmid vs on the bacterial chromosome, and the relatedness of travel-acquired CTX-M-EC plasmids to previously sequenced plasmids. METHODS: Faecal samples were collected pre- and post-travel from 23 volunteers who visited South Asia, and CTX-M-EC were cultured. After short- and long-read sequencing, 10 plasmid sequences were identified and compared with previously sequenced plasmids in GenBank. Conjugation to E. coli K-12 was undertaken using filter mating. FINDINGS: Thirty-five percent of CTX-M-EC isolates tested transferred the blaCTX-M plasmid by conjugation. Travel-acquired CTX-M-EC carried blaCTX-M on a plasmid in 62% of isolates, whereas 38% of isolates had blaCTX-M on the chromosome. CTX-M-EC plasmids acquired after travel to South Asia had close homology to previously described epidemic plasmids which are widely disseminated in humans, animals and the natural environment. CONCLUSION: Globally successful epidemic plasmids are involved in the spread of CTX-M-EC. Targeted strategies may be used to displace such plasmids from the host strain as part of efforts in infection prevention and control in healthcare settings. Bacteria with blaCTX-M plasmids were readily acquired by healthy volunteers, and were carried on return to the UK, providing opportunities for onward dissemination.